Essential Science: Mystery of Mercury’s Great Valley

Mercury has long been regarded as one of the Solar System’s more mysterious planets. Despite decades of observations by astronomers new points of interest appear. The latest is with the planet’s great valley.

The new insight into the planet located closest to the Sun has come from NASA’s MESSENGER spacecraft. This relates to a valley located on the planet’s surface and the reason for its formation is linked to the planet having shrunk at some point in the past.

MESSENGER is an acronym for MErcury Surface, Space ENvironment, GEochemistry, and Ranging; the word also serves as a reference to the Roman mythological messenger, Mercury. While in orbit around Mercury the spacecraft was powered by a two-panel gallium arsenide/germanium solar array.

The spacecraft orbited the planet Mercury between 2011 and 2015. The data from the probe is still being analysed. The most recent review of the collected data indicates that Mercury’s only tectonic plate has deformed.

While Mercury has often been viewed from afar there have been very few space probes sent close to the planet. The reason why so few missions have targeted Mercury is because it is very difficult to obtain a satellite orbit around the planet on account of its proximity to the Sun.

These images of Mercury were taken onboard the MESSENGER spacecraft, the first ever to orbit the innermost planet.

A person’s weight on Mercury would only be 38 percent of their weight on Earth.

A year on Mercury takes 88 Earth days.

Mercury is the most cratered planet in the Solar System.

Mercury has a diameter of 4,879 kilometers, making it the smallest planet.

It is not known who discovered Mercury.

Mercury is the smallest and innermost planet in the Solar System, with an orbital period of just 88 Earth days. Mercury is composed of a rocky body like Earth with a high iron content, and the planet probably has a molten core. One notable feature about Mercury's surface is the presence of numerous narrow ridges, extending up to several hundred kilometers in length.

The recent findings about structural changes to Mercury has come about due to MESSENGER allowing the researchers to generate stereo images of the planet’s surface. These images have highlighted what is being termed the Great Valley. This is a ravine stretching about 620 miles long, 250 miles wide, and two miles deep. The valley stretches into the Rembrandt basin, which is the youngest of the impact craters on the planet’s surface.

This diagram shows the approximate relative sizes of the terrestrial planets, from left to right: Mercury, Venus, Earth and Mars. Distances are not to scale.

NASA Mercury image: JHUAPL Venus image: JPL Mars image: HST

The valley is shown and described in the following video:

With the video from NASA, the image mosaic transforms into a colorized digital elevation model created from stereo images of the region.

The valley is interesting since it relates to Mercury’s lithosphere (the region between the crust and its upper mantle). These conditions differ to Earth in that there is only one tectonic plate. The lithosphere describes the rigid outermost shell of a planet, which is normally broken up into several tectonic plates (the Earth has seven).

Since Mercury only has one tectonic plate, the internal cooling within the planet probably led to its only plate to contort and bend. Here, as Laboratory Reports notes, some sections of the planet were forced upward and other parts were forced to sag inward.

The analysis from the space probe indicates that the Great Valley on Mercury is the result of the global contraction of a shrinking one-plate planet. This has surprised analysts from NASA.

The research indicates that each planet, even those seemingly similar to earth, have different geologies and have undergone different developments. Since temperature changes inside the planet are on-going further buckling is likely to occur.

The research into Mercury has been published in the journal Geophysical Research Letters. The paper is titled “Fault-bound valley associated with the Rembrandt basin on Mercury.”

This article is part of Digital Journal's regular Essential Science columns. Each week Tim Sandle explores a topical and important scientific issue. Last week we examined research about a gene that could prevent people from drinking excessively. The week before considered the role of nitrogen in the diet and the impact of this upon gut health.